1. Field of the Invention
The present invention relates to an anti-theft system for a vehicle.
2. Description of Related Art
There have been various anti-theft systems for vehicles. One of the anti-theft systems that is rapidly becoming popular employs an anti-theft control unit called an immobilizer (a first control unit) that cooperates with an engine control unit (second control unit) for controlling engine operation such as fuel injection and ignition timing.
One of the anti-theft systems of this type which employ immobilizers is known from, for example, Japanese Unexamined Patent Publication No.10-53106. This prior art anti-theft system comprises key code read means for reading a first key code or individual key code identifying an individual key that is inserted into an ignition switch of a vehicle equipped with the anti-theft system, a first control unit (immobilizer) operative to receive a signal representative of the first key code through the key code read means and a second control unit that controls operation of the engine such as fuel injection and ignition timing. When the ignition switch is turned on, the second control unit sends a request signal to the first control signal so as to cause the first control unit to start reading in the first key code. The first control unit collates the first key code with a second key code or reference key code that the first control unit stores in a memory. When the first key code agrees with the second key code, the key is justified as an intrinsic key for the vehicle, then, the first control unit sends back an instruction of approval (which is hereafter referred to as an approval instruction) to the second control unit so as to permit the engine to operate. On the other hand, when the first key code disagrees with the second key code, the key is denied to be intrinsic, then, the first control unit sends back an instruction of refusal (which is hereafter referred to as a refusal instruction) to the second control unit so as to prohibit the engine from operating.
The prior art anti-theft system disclosed in the publication mentioned above takes a comparatively long time before the first control unit provides the second control unit with an instruction, an approval instruction or a refusal instruction, because the first control unit starts a collation between the first and second key codes after receiving a request signal from the second control unit. This leads to a waste of long time before an engine start-up even when an intrinsic key is duly used. In order to shorten a time wasted before an engine start-up when the intrinsic key is used, it can be thought to activate the first control unit prior to activation of the second control unit so as to perform a collation between these first and second key codes in advance. In such a case, however, the second control unit is possibly still in an inactivated condition when the first control unit sends an instruction on the basis of a result of the collation to the second control unit. In light of reliable anti-theft properties, there is still room for improvement in the advance collation of the first and second key codes.
Another anti-theft system of this type which employs immobilizer is known from, for example, Japanese Unexamined Patent Publication No. 8-80811. This prior art anti-theft system includes a cut-off relay that is closed by the first control unit to supply power to a starter motor of an engine and is opened by the first control unit to shut off the power supply from the starter motor of the engine. Specifically, while the first control unit closes the cut-off relay so as to start the starter motor when a collation between the first and second key codes results in agreement, the first control unit opens the cut-off relay so as to prohibit the starter motor from starting up when a collation between the first and second key codes results in disagreement, thereby increasing the anti-theft property. In light of anti-theft properties, the anti-theft system puts the second control unit inoperative upon activation thereof and the cut-off relay left opened in its initial condition.
According to the anti-theft system, when the engine stalls for some reason or other, such as, for example, a short break in power supply to the second control unit due to noises and/or vibrations, a comparatively long time is spent before the engine is restarted up. That is, since, when trying to restart up the engine after an occurrence of a short break in power supply to the second control unit, the first control unit that continues normal operation holds the cut-off relay closed, the second control unit does not permit the engine to operate unless the first control unit provides the second control unit with another approval instruction even though the starter motor operates. This is because the second control unit is prohibited from being activated upon reactivation after a short break in power supply thereto.
It is an object of the present invention to provide an anti-theft system for a vehicle of a type adapted to provide a second control unit with an instruction, an approval instruction or a refusal instruction, from a first control unit on the basis of a result of a collation of a first key code identifying an individual key and a second key code stored as a reference key code in the first control unit.
It is another object of the present invention to provide an anti-theft system for a vehicle which takes only a short time before providing a second control unit with an instruction, an approval instruction or a refusal instruction, and provides the second control unit with high reliability in recognizing the instruction.
It is another object of the present invention to provide an anti-theft system for a vehicle which shortens a time spent on restarting the engine after an engine stall that is caused by deactivation of a second control unit due to a short break in power supply thereto.
The above objects are achieved by an anti-theft system for a vehicle which comprises a first control unit operative to read in a first key code, namely a key code of an individual key through key code signal receiving means and a second control unit operative to control operation of an engine of the vehicle. The first control unit comprises first memory means for storing data of a second key code as a reference key code of an intrinsic key exclusive to the engine therein, collation means for making a collation between the first key code and the second key code in the first memory means so as to determine agreement or disagreement between the first and second key codes before activation of the second control unit, second memory means such as to hold data therein upon an occurrence of a short break in power supply thereto, for storing data of a result of the collation therein, detection means for detecting activation of the second control unit, and control means for, when the detecting means detects activation of the second control unit, providing the second control unit with an approval instruction that approves operating the engine when the collation results in agreement between the first and second key codes and with a refusal instruction that refuses operating the engine when the collation results in disagreement between the first and second key codes.
With the anti-theft system, the first control unit performs a collation between the first and second key codes prior to activation of the second control unit and memorizes a result of the collation. Further, the first control unit provides the second control unit with an instruction, an approval instruction or a refusal instruction, according to the result of the collation after detection of activation of the second control unit. This shortens a time wasted before providing the second control unit with the instruction, in particular, in the event where an intrinsic key exclusive to the engine of the vehicle is used. The anti-theft system makes it reliable that the second control unit receives an instruction, in particular, in the anti-theft viewpoint, a refusal instruction when a false key is used, so as to satisfactorily perform the anti-theft function. The use of the second memory that holds data therein upon an occurrence of a short break in power supply to the first control unit guarantees the result of collation between the first and second key codes even though there occurs a short break in power supply due to noises and vibrations.
In the anti-theft system, the second control unit may provide the first control unit with a request signal both upon the activation of the second control unit and when the engine attains a specified speed of rotation. In this case the first control unit provides the second control unit with either one of the approval instruction and the refusal instruction in response to receipt of the request signal. Even when the first control unit provides the second control unit with neither an approval instruction nor a refusal instruction upon a start-up of the engine while the second control unit is left unjustly activated by a false key, the second control unit receives an instruction all over again in response to a request signal that the second control unit sends to the first control unit when the engine attains the specified speed of rotation. Accordingly, while the engine continues operation when the key is intrinsic and is, however, stopped when the key is false. This reliably prevents the vehicle from being stolen.
The first control unit may be forcibly activated when the first control unit remains inactivated upon provision of the request signal by the second control unit when the engine attains the specified speed of rotation. Further, the second control unit may be inactivated when the first control unit remains inactivated upon provision of the request signal by the second control unit when the engine attains the specified speed of rotation. These variants make it reliable to prevent the vehicle from being stolen when a false key is used to start up the engine.
Upon receipt of the request signal by the first control unit when the engine attains the specified speed of rotation, the first control unit may read in a first key code so as to make a collation between the first key code and the second key code. The second control unit is provided with either one of the approval instruction and the refusal instruction according to a result of the collation between the first key code read upon receipt of the request signal when the engine attains the specified speed of rotation and the second key code. This variant makes it more reliable to prevent the vehicle from being stolen when a false key is used to start up the engine.
The first control unit may prohibit the collation between the first key code and the second key code when failing to read in the first key code while a key is out of an ignition position and forcibly treat a result of the collation between the first key code and the second key code as disagreement when failing to read in the first key code while the key is in the ignition position. This prevents the first key code from being judged to disagree with the second key code when the intrinsic key is left half inserted in the ignition switch. In other words, this prevents an unsuccessful start-up of the engine when the intrinsic key is used. When a turn of a key is detected, it is judged that a position occupied by the key is for permitting a start-up of the engine. In such a case, the collation is treated as disagreement when a first key code fails to be read in. This variant makes it reliable to prevent the vehicle from being stolen.
The first control unit may be adapted to try to read in a first key code either a predetermined number of times or for a predetermined period of time when failing to read in the first key code when there is no turn detected and discontinue reading in the first key code when failing to read in the first key code even after the predetermined number of trials. This, on one hand, increases the possibility of regularly reading in a first key code and, on the other hand, decreases the consumption of electricity due to a repeat of the reading of first key code.
According to another preferred embodiment, the anti-theft system further comprises a cut-off relay operative to supply power to a starter motor of the engine when closed and to shut off the power from the starter motor when opened. The first control unit holds the cut-off relay open in an initial condition thereof. Because the cut-off relay is prevented from closing unless the first control unit recognizes agreement between the first and second key codes, the engine is prevented from being started up by a false key. This provides an increased reliability of the anti-theft system.
In this embodiment, the first control unit may provide the second control unit with either one of an approval instruction and a refusal instruction only upon reception of the request signal from the second control unit. Even when there occurs temporary disagreement between first and second key codes due to a short break in power supply to the first control unit, the second control unit prevents the engine from continuously remaining stopped due to the temporary disagreement the second control signal provides the first control unit with a request signal. This advantageously prevents or significantly reduces an occurrence of an accidental engine stall while the vehicle travels.
The first control unit may read in a first key code at a specified timing at a specified period so as to periodically make a collation between the first key code read in at the specified timing and the second key code. In this case, the second memory means replace the data of a precedent result of the collation with data of a result of the collation between the first key code read at the specified timing and the second key code. According to this anti-theft system, the first control unit provides the second control unit with an instruction according to updated data of a result of the collation, so that, even when the engine can be started up by activating the second control unit by the use of a false key, the engine is immediately stalled by virtue of the periodic collation. This improves the anti-theft properties.
The second control unit may be prevented from being inactivated immediately at least when the periodic collation results in disagreement. This avoids an occurrence of an accidental engine stall while the vehicle travels and brings the engine into stall at a desired timing. Further, first control unit may be provided with a cut-off relay that supplies power to a starter motor of the engine when closed and shuts off the power supply from the starter motor when opened. The first control unit controls the cut-off relay to close when the collation results in agreement between the first key code and the second key code so as to permit the starter motor to operate and to open when the collation results in disagreement between the first key code and the second key code so as to prohibit the starter motor from operating. According to the anti-theft system, while the cut-off relay that is opened when the collation results in disagreement improves the anti-theft properties, the starter motor can be put in a start immediately upon restarting the engine after an engine stall while the vehicle travels. This is preferable for the engine to restart.